1. Field of the Invention
This invention relates to a light-sensitive composition which can be used for preparation of a lithographic printing plate, a resist for forming a printed circuit, a color filter and a phosphor pattern, particularly to a light-sensitive composition suitable for a lithographic printing plate. More specifically, it relates to a light-sensitive composition which is capable of forming an image by using a scanning exposure device such as laser, etc. Also, it relates to a lithographic printing plate which is capable of mounting to a printing machine without carrying out development and of printing.
2. Prior Art
As a light-sensitive composition capable of developing with water, there has been used, for example, a light-sensitive composition in which a dichromate is added to a water-soluble polymer such as gelatin, polyvinyl alcohol and the like as a material for color filter. However, it involved a problem in a treatment of a disposed liquid containing a chromate, so that other various systems have been investigated in place of the above light-sensitive composition.
One of which is a water-developable light-sensitive material utilizing a polymer in which a quaternary ammonium salt compound such as a styryl pyridinium salt compound and a styryl quinolinium salt compound is condensed to polyvinyl alcohol as disclosed in Japanese Patent Publications No. 5761/1981and No. 5762/1981, and Japanese Provisional Patent Publication No. 11906/1981.
However, such a composition cannot show sufficient characteristics in resolution and sensitivity.
On the other hand, a light-sensitive material in which a water-soluble azide compound and a water-soluble polymer capable of crosslinking by the compound are combined has been well known. As the water-soluble polymer in this case, there are disclosed a polyvinyl alcohol-maleic acid copolymer in Japanese Provisional Patent Publication No. 97602/1973 and a polyvinyl alcohol-acrylamide copolymer in Japanese Provisional Patent Publication No. 97603/1973, but they are low sensitivity. Similarly, as disclosed in Japanese Provisional Patent Publication No. 90185/1973, when polyvinylpyrrolidone is used as a water-soluble polymer, relatively high sensitivity with a certain extent can be obtained but it is insufficient. Also, in a system using a poly (meth)acrylamide-diacetone acrylamide copolymer as disclosed in Japanese Patent Publication No. 20225/1977 or Japanese Provisional Patent Publication No. 2000-248027, the resulting material is insufficient in resolution and sensitivity.
To accomplish high sensitivity, an example in which a light-sensitive azide group is introduced into a water-soluble polymer itself has been disclosed, for example, in Japanese Provisional Patent Publications No. 185163/1997 and No. 84655/1999, but it is difficult to obtain a material excellent in both of high sensitivity and preservation stability, and the material cannot be used practically.
Similarly, an example of a light-sensitive composition capable of subjecting to water-development by incorporating a polymerizable unsaturated group to a side chain of polyvinyl alcohol and using a photopolymerization initiator has been disclosed in Japanese Provisional Patent Publication No. 2000-181062 to obtain a high sensitivity material. In this case, the group having the polymerizable unsaturated group incorporated into the side chain is introduced as a side chain of the polyvinyl alcohol by an acetal reaction. Thus, when an incorporation ratio is increased to heighten sensitivity, water-solubility of the resulting polymer is decreased whereby there is a problem that water-developability is lowered.
Moreover, when the above-mentioned water-developable light-sensitive composition is intended to use for a lithographic printing plate, an image portion after development is extremely poor in lipophilic property, and image strength is weak since it is swelled by water, so that it cannot endure for usual lithographic printing.
Also, in Japanese Patent Publication No. 13020/1980, a light-sensitive composition using a cationic water-soluble polymer having an unsaturated group. The light-sensitive composition of said publication utilizes photodimerization of unsaturated double bonds, and this is similar reaction mechanism as photodimerization of cinnamic acid or styryl pyridinium salt. This reaction mechanism of the photodimerization does not interpose a photopolymerization initiator or a photo-acid generator. Accordingly, this is different from a cross-linking reaction inevitably using a photopolymerization initiator or a photo-acid generator of the present invention, and the constitution of the present invention is never described in the above publication. Also, the light-sensitive composition of said publication is only sensitized by ultraviolet rays. Moreover, it is low sensitivity since no amplification process is contained and high energy is required for exposure, and further it has no sensitivity to light in the region of visible rays to near infrared rays, so that it cannot correspond to an output machine using a laser beam mentioned below.
In Japanese Provisional Patent Publication No. 101620/1997, a light-sensitive resin composition using a polymer having a cationic group and a (meth)acryloyl group at a side chain has been disclosed. This is a printing plate material corresponding to flexographic printing, and there are problems that water-developability is poor and development requires for a long period of time. Moreover, when said light-sensitive composition is used for a lithographic printing plate, there are problems that ink-adhering property and printing endurance are poor.
In the field of a lithographic printing plate, according to progress of an image forming technique in recent years, a light-sensitive composition showing high sensitivity to visible rays has been desired. For example, research on a light-sensitive composition and a lithographic printing plate which correspond to an output machine using argon laser, helium-neon laser, red color LED and the like have actively been carried out.
Moreover, according to remarkable progress in a semiconductor laser, a near infrared laser light source of 700 to 1300 nm has been easily utilized, so that a light-sensitive composition and a lithographic printing plate which correspond to said laser light have been attracted attention. In addition, an image drawing device (a plate setter) utilizing a near infrared semiconductor laser emitting at around 400 nm has been commercially available, and a high sensitivity light-sensitive composition and a lithographic printing plate capable of forming an image (making plate) by the device have been desired to be developed.
As a photopolymerizable composition having light-sensitivity at the above visible rays to near infrared rays, there is disclosed a lithographic printing plate containing a compound which is capable of subjecting to radical polymerization and has an ethylenically unsaturated bond, a photosensitizing dye having an absorption peak at 400 to 500 nm and a polymerization initiator in Japanese Provisional Patent Publication No. 134007/1997. Also, a combination of an organic boron anion and a dye is disclosed in Japanese Provisional Patent Publications No. 143044/1987, No.150242/1987, No.5988/1993, No.194619/1993, No.197069/1993 and No. 2000-98603; a combination of a dye and an s-triazine type compound is disclosed in Japanese Provisional Patent Publications No. 31863/1992 and No. 43633/1994; a combination of a resol resin, a novolac resin, an infrared absorber and a photo-acid generator is disclosed in Japanese Provisional Patent Publications No. 20629/1995 and No. 271029/1995; and a combination of a specific polymer, a photo-acid generator and a near infrared sensitizing dye is disclosed in Japanese Provisional Patent Publications No. 212252/1999 and No. 231535/1999. Moreover, a light-sensitive composition using a polymer having a phenyl group substituted by a vinyl group is disclosed in Japanese Patent Publication No. 105353/1994 and Japanese Provisional Patent Publication No. 2001-290271.
However, in either of the above-mentioned examples, a binder polymer to be used in the light-sensitive layer is not water-soluble. When development is carried out, a strongly alkaline developing solution (a pH of which exceeds 10) dissolved therein a strongly alkaline compound such as sodium hydroxide, potassium hydroxide, potassium silicate and the like, so that development with water can hardly be carried out. Also, it is necessary to carry out development by using an automatic developing device for exclusive use.
To the contrary, a lithographic printing plate capable of effecting water-development or requiring no development itself is desired to be developed. For example, a non-treatment printing plate without requiring development which utilizes abrasion-removal of a binder polymer by irradiating a high output near infrared semiconductor laser has been proposed. For example, in Japanese Provisional Patent Publication No. 48018/1996, there is disclosed a method of preparing a lithographic printing plate by removing an ink-receptive polymer by abrasion and exposing a surface of a hydrophilic support by a cleaning agent. However, it causes grounds or scum remained after abrasion (which is so-called “debris”) which causes optical contamination or background stain of a printing plate in some cases.
As other attempts, an example of a water-developable and heat-sensitive lithographic printing plate which utilizes the above-mentioned high output near infrared semiconductor laser, provides a layer containing thermoplastic polymer fine particles as a heat-sensitive layer and makes water-insoluble by fusing polymer fine particles utilizing higher heat generating at a laser irradiating portion is disclosed in Japanese Provisional Patent Publications No. 171250/1997, No. 186646/1998 and No. 265062/1999, and U.S. Pat. No. 6,001,536. This is a preferred system since development can be carried out on a printing machine by feeding dampening water but there are problems that sensitivity to laser light is low and background stain likely occurs.